Just like physical appearance affects the way many humans act around others, sometimes even boosting an individual’s confidence, certain birds have been found to act in a similar manner. A recent study by the University of Colorado Boulder and Cornell University shows that the physiological health of North American barn swallows is highly dependent on the hue of their feather color.

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Led by CU-Boulder’s Assistant Professor Rebecca Safran, a 2008 study showed that male barn swallow testosterone sharply increased when researchers artificially enhanced their breast colors during breeding season. Similarly, a new study performed on female barn swallows showed that birds with both naturally darker and artificially darker breast feathers had lower levels of oxidative damage, potentially leading to healthier birds. According to Cornell Senior Research Associate Maren Vitousek, oxidative stress results when the production of harmful metabolites known as free radicals exceeds antioxidant defenses in birds, leading to DNA, protein, and fat damage.

60 female barn swallows were captured with mist nets in Boulder and Jefferson counties near Denver for the new study. Half were used as a control group while the Vitousek, Safran, and a team of undergraduate and graduate students darkened the plumage using a non-toxic marker on the remaining thirty birds. The testosterone, oxidative damage, and antioxidant levels of all birds were measure at that time. The birds were then released back into the wild.

"Between one and three weeks later, 19 of the artificially darkened females and 17 birds from the control group were recaptured, re-tested for testosterone, oxidative damage and antioxidant levels and then released back into the wild," said Vitousek.

"Intriguingly, females whose feathers were darkened to resemble ”˜attractive’ birds rapidly adopted the physiological state of darker birds, decreasing their level of oxidative damage," said Vitousek. "These results suggest the appearance of an individual may be an under-appreciated driver of physiological health."

According to Safran, "Although there is evidence that breast feather color is significantly influenced by genetics, melanin-based plumage color like that in barn swallows also has been tied to social status and even to circulating testosterone."

Both studies have shown that an individual bird’s appearance is often a sign of a physiological condition, health and status.